Many photographic materials, particularly color negative films, contain so-called DIR (development inhibitor releasing) couplers. In addition to forming imaging dye, DIR couplers release inhibitors that can restrain silver development in the layer in which release occurs as well as in other layers of a multilayer photographic material. DIR couplers can help control gamma or contrast, can enhance sharpness or acutance, can reduce granularity and can provide color correction via interlayer interimage effects.
To provide suitable inhibition of silver development and the desirable photographic effects thereof, a DIR coupler must release an inhibitor that effectively interacts with silver and/or silver halide during development. In addition to being of the proper structural type, the inhibitor must have the proper degree of hydrophobicity to retard efficiently silver development. One measure of hydrophobicity that has been related to inhibitor strength is log P, the octanol/water partition coefficient, for the inhibitor. The relationship between inhibition and log P is described in R. P. Szajewski et al. "Progress in Basic Principles of Imaging Systems", F. Granzer and E. Moisar, eds., Vieweg & Sohn, Braunschweig, 1987, p 425 and in U.S. Pat. Nos. 4,782,012, and 5,006,448. An inhibitor becomes more hydrophobic as log P increases. An inhibitor also becomes more hydrophobic as the number of carbons in an alkyl chain increases or as the number of chlorine substituents increases, since both methylene and chlorine groups are relatively hydrophobic. If the degree of hydrophobicity of the inhibitor is too low it will not effectively inhibit silver development, thus inhibitors with low log P values or insufficient numbers of carbon atoms or chlorine atoms tend to be inefficient. Addition of thioether groups to an alkyl chain tends to enhance interactions with silver and silver halide, and thus allows compounds with somewhat lower log P values or fewer numbers of carbon atoms to be effective inhibitors. If log P or hydrophobicity of a prospective inhibitor becomes too high, its effectiveness also tends to be diminished, since it may become so insoluble in the aqueous processing solution that most of it remains in dispersion droplets rather than diffusing to silver or silver halide particles. Inhibitors that are too hydrophobic also tend to deliver little interlayer interimage, since little inhibitor can diffuse out of the layer in which it is generated.
U.S. Pat. No. 4,182,630 broadly discloses triazole-releasing DIR couplers, including DIR couplers having 1,2,4-triazole coupling-off groups with 3-carboxy acid ester substituents (R.sub.2) having 1-18 carbon atoms in the alkyl chain. However, such couplers are relatively ineffective DIR couplers that produce minimal inhibition of silver development. U.S. Pat. No. 3,933,500 also broadly discloses couplers with triazole coupling-off groups.